# Physiology of Photoreceptors

> **NIH NIH R01** · UNIVERSITY OF CALIFORNIA LOS ANGELES · 2020 · $390,000

## Abstract

Project Summary/Abstract
Visual experience begins with electrical responses of retinal photoreceptors. Only light detected
by rods and cones can be analyzed by higher visual centers to alter our behavior. It is therefore
essential that we understand how photoreceptors convert light into changes in membrane
potential and how the mechanism of transduction is modulated in steady illumination. Although
research during the last 30 years has clarified many features of photoreceptor biochemistry and
physiology, most of this work has been done on rods, even though cones respond over a much
wider range of intensities and are more important for visual perception. Cones have the
remarkable ability to continue to respond even in bright light; unlike rods, cones never saturate
no matter how strong the background illumination. Cones can continue to adjust sensitivity so
that it remains proportional to ambient illumination, maximizing the detection of contrast even
in light bleaching a significant fraction of the visual pigment. Moreover background light
accelerates the recovery of the cone response, enhancing the sensitivity of the visual system to
change and motion when light is no longer limiting. An understanding of adaptation is essential
to any effort to replace visual function in degenerated retina with some form of extrinsic light
detector. We cannot hope to restore the ability of vision to operate over an extensive range of
light intensities unless sensitivity and response kinetics can be made to adapt to the ambient light
intensity. Failure of photoreceptors to adapt or recover normally can lead to genetically inherited
retinal diseases including night blindness, bradyopsia, Oguchi disease, and Leber’s amaurosis.
For this reason, the Retinal Disease Program of the NEI has as one of its program objectives to
“analyze the mechanisms underlying light adaptation and recovery following
phototransduction”. The goal of this research is to understand the effects of steady background
light and bleaching on sensitivity and response recovery in mammalian cones, in order to test
mechanisms previously postulated for rods and to reveal major gaps in our understanding. These
experiments will exploit an unusually bright LED-based optical stimulator and transgenic
animals to investigate basic properties of mammalian cone physiology; and to combine
measurements of sensitivity modulation by bleaching and steady background light into a
comprehensive explanation of light adaptation.

## Key facts

- **NIH application ID:** 9980382
- **Project number:** 5R01EY001844-44
- **Recipient organization:** UNIVERSITY OF CALIFORNIA LOS ANGELES
- **Principal Investigator:** GORDON Lee FAIN
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $390,000
- **Award type:** 5
- **Project period:** 1984-07-01 → 2021-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9980382

## Citation

> US National Institutes of Health, RePORTER application 9980382, Physiology of Photoreceptors (5R01EY001844-44). Retrieved via AI Analytics 2026-05-26 from https://api.ai-analytics.org/grant/nih/9980382. Licensed CC0.

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